Method of making electric motor rotors



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METHOD OF MAKING AN ELECTRIC MOTOR ROTOR Original Filed Jan. 5, 1942 2 Sheets-Sheet l 132 0622 for MM) [pm/P0 BMW/6;?

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METHOD OF MAKING AN ELECTRIC MOTOR ROTOR Original Filed Jan. 5, 1942 2 Sheets-Sheet 2 In yen for g9 METALWORKING.

Patented Sept. 11, 1945 UNITED STATES PATENT OFFICE METHOD OF MAKING ELECTRIC MOTOR ROTORS Harry Edward Pancher, Owosso, Mich., assignor to A. G. Redmond 00., Owosso, Mich., a corporation of Michigan 8 Claims.

This application is a division of my copending application Serial No. 425,668, filed January 5, 1942, and entitled Motor rotor and method of making the same, and pertains broadly to a method of producing the improved electric motor and rotor illustrated and described in said c0- pending application and likewise illustrated and described hereinafter in the present application. More particularly and specifically the invention pertains to a method of producing an electric motor rotor which has a plurality of inductor bars each of which extends longitudinally of the rotor and is disposed at an angle to the longitudinal axis of the rotor, such as for example a rotor suitable for and highly efficient for use in a shaded pole induction motor.

The utilization of the present process has the hereinafter enumerated advantages and enables the production of a motor rotor having the hereinafter enumerated desirable attributes.

One of the primary objects of the invention is to simplify and cheapen the manufacture of the rotor.

Another object of the invention is to provide not only an improved rotor but a rotor which will produce an improved motor in that the motors having incorporated in them a rotor of my construction will have more uniform performance and be free from magnetic hum.

In the accomplishment of the foregoing objects and advantages other specific advantages are obtained such as definite assurance of the maintenance of the proper angle or disposition of the inductor bars; material if not complete elimination of the rejection of rotors due to imperfection in manufacture or in performance; and the elimination of certain manufacturing steps heretofore necessary in the production of rotors as well as other objects which will appear from the following specific description.

Accomplishment of the foregoing objects and advantages have resulted in the creation of a new and improved method in the manufacture of rotors as well as the creation of inductor bars having a, novel and improved construction.

In the accompanying drawings which illustrate an embodiment Of the present invention and a rotor built in accord with the present imr 'toved method:

Fig. 1 is a side plan view of an electric motor.

Fig. 2 is a side or plan view of the improved rotor.

Fig. 3 is an end view of the rotor partly in vertical section on a line between two of the rotor plates as is intended to be indicated by the section line 3-3 of Fig. 2 of the drawings.

Fig. 4 is a diagrammatic plan or side view illustrating the manner of mounting the inductor bars in the rotor plates, only the end rotor plate being illustrated for the purpose of clearer understanding.

Fig. 5 is a fragmentary detail view of several of the inductor bar slots in a rotor plate with an inductor bar illustrated in vertical sectional view, the view indicating the condition of these parts prior to the machining operation.

Fig. 6 is a view similar to Fig. 5 after the rotor has been subjected to a machining operation.

Fig. 7 is a detail perspective view of one of the inductor bars.

Fig. 8 is a plan view of one of the end plates of the rotor, the bent-over ends of several inductor bars being shown in dotted lines.

Fig. 9 is a vertical sectional view through the rotor with the end plates in place prior to scouring the end plates and protruding ends of the inductor bars together.

Fig. 10 is a fragmentary plan view of the end of the rotor illustrating the manner of bending the ends of the inductor bars.

Fig. 11 is a side view of a modified form of inductor bar.

Fig. 12 is a vertical sectional view taken on the line l2l2 of Fig. 11.

To a complete understanding of the advantages and benefits attendant to my improved motor rotor and the method of making the same, a short discussion and description of a conventional rotor and the method of making the same is necessary.

The conventional or ordinary rotor commonly found in electric motors comprises a shaft which is knurled or roughened intermediate its ends and for a distance along the shaft equal or substantially equal to the length of the desired rotor. The rotor itself is laminated and the metal plates of which it is composed are circular in form and provided with a passageway of the proper shape to permit the passage therethrough of the rotor shaft and of the proper dimension to require a force fit with the knurled portion of the shaft so that the plates are held against axial rotation on the shaft through frictional engagement with the knurled portion of the shaft.

In spaced relationship throughout their circumferences the plates are provided with openings having a closed bottom, and an open top which is of reduced size and extends to and terminates at the peripheral edge of the plates. These openings are for the reception of the inductor bars of the rotor which bars are composed of metal and are of a length greater than the length of the rotor so as to protrude or extend beyond the rotor at both ends thereof.

In mounting or positioning the plates constituting the rotor proper on the shaft the inductor openings are aligned in a manner to properly receive the inductor bars which instead of being straight throughout their lengths are twisted which twist or skew is of material importance in producing motors which will have uniform performance and will not have in them magnetic hum. Consequently the maintenance of the angle of the skew of the inductor bars is of prime importance.

From the foregoing it will beunderstood that although the inductor bars extend in a direction longitudinal the axis of the rotor and the rotor shaft the inductor bars do not parallel the shaft by reason of their being twisted.

For the purpose of obtaining different performance characteristics the size, and by size I have reference to thickness, of the inductor bars are different with the result that while in some rotors the inductor bars may practically fill the inductor openings or slots in the rotor plates in other instances where the size of the bars is reduced they fit quite loosely in the slots.

It will be obvious that where the inductor bars fit loosely in their slots they cannot lock or hold the rotor plates against axial rotation on the rotor shaft. The only means tending to prevent rotation of the plates on the shaft is their frictional engagement with the roughened or knurled portion of the shaft, and I have found that this frictional engagement between the shaft and the plates is not sumcient to maintain the rotor plates against axial rotation when the rotor is subjected to those operations which it must undergo to become a completed and finished rotor. Should the plates rotate axially the angle of the skew of the inductor bars is not maintained and therefore uniformity of performance of the motors is destroyed and the motors have in them a magnetic hum.

When an assembly has been made of the rotor plates on the shaft with the inductor bars extending through the plate slots the rotor must be subjected to a machining operation. It is the face or outer surface of the rotor which is machined and it is during this machining operation that the plates are subjected to a strain which causes them to rotate on the shaft in respect to one another and thus destroy the angle of the skew, that is the proper angle of the inductor bars.

Furthermore it has been usual practice to provide rotors which have at their outer face or surface a gap or groove which extends from edge to edge of the rotor. This gap or groove is occasioned by the reduced open tops of the plate inductor slots by reason of the fact that no portion of the inductor bars are disposed within the opening at the top of the slots.

I have found that this opening or groove interferes materially with the production process incident to the manufacture of rotors for the reason that when the rotor is subjected to the hereinbefore described machining operation metal shavings as well as other material from the body of the rotor are turned over and down into this opening or groove. By reason of the foregoing it has been necessary in the past to reject many rotors due to irregularities in the groove and by reason of shavings or chips being present in the grooves and which when present have a tendency to be drawn out of the grooves by the magnetism generated in the stator when the motor was running. I have fOllIld that due to the presence of irregularities or foreign matter in the grooves motors have been noisy and there has not been uniformity of performance.

It will be obvious that the preceding described deficiencies and objections would not only result in an increase of the cost of production but would likewise result in the production in many instances of noisy motors and motors which are not uniform of performance.

In the past it has not been unusual practice after the rotor had been machined to subject it to a varnishing operation to seal the grooves in its face so as to prevent the metal shavings, chips or other foreign matter from being drawn out from the grooves. This practice has not been found altogether satisfactory and has been discontinued and when used constituted a step which increased the cost and reduced the speed of production.

It has been mentioned that the inductor bars protrude and it has been common practice to melt or fuse down the extending portions of the inductor bars upon or over the ends of the rotor.

Having the foregoing deficiencies of rotors as now made as well as the difllculty of manufacturing them in mind and desiring to overcome the same I have conceived an improved rotor and the method of making the same, a specific description of which is as follows.

Having reference to the accompanying drawings and utilizing similar reference characters and numerals to designate like parts throughout the description, I designates the rotor shaft which throughout a portion of its length is roughened or knurled as at 2.

The motor as an entirety is designated by A and appears in Fig. l of the drawings. As is conventional the motor comprises a two-piece housing the parts of which are designated as 3 and 4 and within which the parts making up the motor are disposed on and about the motor shaft I which passes completely through the housing.

The rotor as an entirety in its finished form is illustrated in Fig. 2 and designated as an entirety by B.

The rotor is laminated and made up of a plurality of metal plates 5 each of which is provided centrallym g for the passage of the rotor shaft and for frictional engagement, as illustrated in Fig. 3 of the drawings, with the knurled or roughened portion 2 of the shaft. These plates are arranged in face to face abutting relationship on the shaft and the number of plates used is of course determined by the desired length of the rotor just as the diameter of the plates is determined by the desired diameter of the rotor.

Each of the rotor plates in spaced relation around its circumference is provided with a plurality of inductor bar slots 0 each having a closed rounded bottom 1 and an open top 8 the size of which is materially reduced as respects the transverse size of the slot. By reference particularly to Fig. 5 of the drawings it will be seen that the open top or opening at the top of the inductor bar slot extends all the way to and through the peripheral edge 9 of the rotor plate.

The inductor bars. which are composed of copper or other suitable metal, are designated as an entirety by D and their configuration can be clearly determined by reference to Fig. '7 of the drawings in conjunction with Fig. 5 of the drawings wherein an inductor bar appears in vertical cross section.

Fig. 4 of the drawings is diagrammatic in nature and is included for the purpose of more clearly illustrating the invention and to that end only the two outer rotor plates making up the rotor are illustrated. From this particular figure it will be seen that the inductor bars are longer than the rotor and that their full sized end portions l and H extend outwardly beyond each end of the rotor. These extending portions l0 and II of the inductor bar, in the finished rotor, are fused or melted down over the end of the rotor as indicated at l2 in Fig. 3 of the drawings.

Each inductor bar has a main portion l3 which is disposed within the inductor slots C of the plates and at its top is provided with an extending fin M of reduced thickness. This fin is of a thickness to freely enter the opening or open top 8 of the plate slot C but sufficient thickness is maintained in the fin to prevent any appreciable looseness between the fin and the opening.

As a result of this construction it will be seen that irrespective of the nature of the fit between the main inductor bar portion 13 and the plate slot C these fins lock the plates together so that they can only rotate on the shaft as a unit. This means that the benefit of the holding power of all of the plates against rotation on the shaft is utilized as against the holding power of the individual plates, as is the case in the prior art practice heretofore specifically described. Furthermore and very important it means that even should the plates rotate axially on the shaft they will rotate as a unit and thus not alter nor destroy the angle of the skew or the angle of the inductor bars.

With this construction it is possible with the same rotor plates to assemble rotors having inductors of varying sizes as respects the thickness or configuration of the main inductor bar portion l3. It remains necessary only to maintain an inductor bar fin of the proper size to fit snugly within the open tops of the inductor plate slots C.

The inductor bars at their lower edges are of reduced thickness to provide a fin 6. This fin like the aforementioned fin [4 has its side walls equally placed from the side walls of the main thickened portion 13 of the bar, that is to say, the fins extend outwardly from the center of the bar in respect to its thickness.

The fin 6 has a definite purpose which is that of engaging the rounded bottoms l of the plates to support the inductor bars so that the fins at their upper edges are in the slot openings 8. Should the full width l3 of the inductor bars be allowed to engage the rounded bottoms 1 of the slots 0 they would engage well up on the radius of these rounded bottoms and this would vary the position of the inductor bars too greatly by reason of the fact that the opening provided by the plurality of slots C is of reduced size by reason of the skew-like extension of the opening caused by the plates 5 having their openings C staggered in respect to one another as they must be to accommodate the bent or curved inductor bars. In other words, the openings provided through the rotor by the slots C of the plates are curved from one end to the other which results in the inductor bars resting on the bottoms 1 of the plates only at the center of the rotor as is illustrated at 20 in Fig. 9 of the drawings.

The result of the foregoing is that with the inductor bars contacting the bottoms of the plate slots only at the center of the rotor these bars will not, unless secured at their ends, remain parallel with the rotor axis but would tend to tilt so as to be high at one end and low at the other.

To prevent tilting of the inductor bars an end plate E is positioned at each end of the rotor and they, like the plates 5, are provided with a central opening 2| to receive the motor shaft I. These plates have a plurality of square openings 22 which equal in number the number of inductor bars and which are of a size to snugly receive the extending end portions l0 and II of the inductor bars. This construction has a decided advantage over endeavoring to build a motor without end rings. These end rings are of copper and therefore it is possible to obtain a. much better connection of the fused ends of the inductor bars through these copper end plates than would be the case were they omitted because when the ends of the inductors are fused or welded the copper end rings provide material for the fused ends of the inductors to flow into and produce a uniform welded end connection. If the ends of the inductor bars are soldered the rings provide a better soldering connection.

When a low resistance and connection is desired several end rings can be used at each end of the rotor.

Additionally these end rings are most important in simplifying the assemby of the motors and this will be apparent from the foregoing remarks pointing out that the openings of the end rings are such as to snugly receive the extending ends of the inductor bars so as to support the bars horizontal to the motor shaft and prevent their tilting with the point 20 as a fulcrum as would occur in assembly were the end plates omitted.

To further assure during assembly the proper positioning of the inductor bars they can be further secured in proper position, if desired, by bending their protruding ends down in a direction opposite to the direction of skew as is illustrated in Fig. 11 of the drawings. Bending of the protruding ends of the inductor bars results in clamping the rotor laminations tighter and assuring the proper positioning of the inductor bars until their ends are fused, welded or soldered to the end plates as they are in the final finished rotor, as is illustrated in Fig. 3 of the drawings.

Maintenance of the inductors in their proper positions parallel with the rotor axis is of the utmost importance in the production of quiet motors.

The production of rotors of different lengths can be simply accomplished by the mere provision of more plates 5 and longer inductor bars. In respect to all rotors the inductor fins will be of a length the same as the length of the stack of abutted plates 5 so that the only protruding parts of the inductors are their full-sized ends l0 and II.

With the plates assembled on the shaft and the inductor bars secured in place the machining operation of the rotor can be safely undertaken and in Figs. 5 and 6 of the drawings I have endeavored to illustrate the rotor before and after being subjected to this machining step. It will be seen that in truing the rotor its original diameter is reduced with the result that a portion of the inductor bar fins I have been removed. It will be further seen that the face l5 of the rotor is smooth and unbroken by any transversely extending gap or groove which of course is due to the fact that the inductor ribs 14 fill the opening constituting the open top of the plate inductor bar slots.

It will be apparent that the characteristics of the motor can be varied by varying the characteristics of the inductor bars. In Figs. 11 and 12 of the drawings a modified form of inductor bar is illustrated and is the type of bar that can be used to obtain a high resistance rotor. The bar is designated as an entirety at F and has a central thick portion 23 which intermediate its ends is notched out as at 24 and 25 to reduce the efiective path through the inductor. At its upper edge the bar is provided with a, fin 26 and at its lower edge, with the exception of the notched out portion, it is provided with a fin made in three separated portions 21, 28 and 29. The center section or portion 30 of the bar is provided to support the bar in the rotor slots. It has been pointed out that the bars are supported on the bottom of the plate slots at a point central of the length of the rotor and accordingly it would not do to notch out the bar central of its length because to do so would remove its means of support in the plate slots.

Thi modified form of rotor can be substituted for the form first described which would not be the case were a bar of small cross section utilized in an effort to provide a high resistance rotor. Additionally a bar of small section would be too thin for practical or safe handling and would weaken the rotor mechanically.

From the foregoing description it will be seen that I have simplified, speeded up and reduced the cost of manufacture of electric motor rotors without in any way sacrificing quality or performance of the rotors, but on the contrary have produced better rotors and as a consequence better motors,

My improved inductor bar also simplifies and cheapens production in that it makes it possible with the same rotor plates to use inductor bars of different size to produce rotors having different performance characteristics. In other words without in any way altering the construction of the laminated rotor different inductor bars can be utilized in combination therewith to produce motors which will have different performance characteristics.

The principle of the invention can be utilized and the improved results of the invention can be obtained without following in specific detail the construction illustrated in the accompanying drawings and consequently the invention is to be limited only within the scope of the hereinafter appended claims.

In the event the end plates were eliminated the melted 0r fused down ends of the inductor bars could be utilized as a substitute therefor to provide in the finished motor conductor plates at the ends of the rotor. Such a construction is not however considered as desirable not only from the standpoint of the finished motor but also from the standpoint of simplifying assembly as is the construction wherein end plates are used, because there would then be no means provided for assuring that the inductor bars are retained in their proper positions during the machining operation to which the rotor must be subjected.

When end plates are used there can be no longitudinal movement whatsoever of the inductor bars because the inductor bar openings in the end plates are not sufiiciently long to permit the passage of the finned upper or lower edges of the bars.

I realize that in the past inductor bars have been cast integral with a rotor and having edges flush with the side and end faces of the rotor, but those constructions are entirely different from my rotor made by assembling the inductor bars therein.

I claim:

1. The method of making an electric motor rotor of the open slot type which comprises, providing a shaft, forming in plates an opening for said shaft of slightly less diameter than that of the shaft and a series of radially extending slots having open ends of reduced width positioned at the outer peripheral face of said plates, forcing a group of said plates on said shaft to provide a laminated core rotatable with said shaft by frictional engagement therewith, arranging said plates so that their slots are in inter-communicating relation to form passageways extending transversely through said core in a plane parallel to the longitudinal axis of the shaft, placing an inductor bar in each of said passageways and making said bars of a size and configuration so that the bottoms of the bars rest upon the bottoms of the slots forming the passageways and the bars are loose in said passageways with the exception of the upper ends of the bars which fit snugly within the reduced width portion of the plate slot outer open ends, machining the outer peripheral faces of said plates to provide a core which is a true circle, and continuing said machining operation until the top edges of the bars and the peripheral faces of the plates are in alignment to provide a rotor which is smooth and unbroken throughout the entire extent of its outer surface.

2. The method of making an electric motor rotor of the open slot type which comprises, providing a shaft, forming in plates an opening for said shaft of slightly less diameter than that of the shaft and a series of radially extending slots having open ends of reduced width positioned at the outer peripheral face of said plates, forcing a group of said plates on said shaft to provide a laminated core rotatable with said shaft by frictional engagement therewith, arranging said plates so that their slots are in inter-communicating relation to form passageways extending transversely through said core in a plane parallel to the longitudinal axis of the shaft but extending at an angle transverse thereof with the result that the bottoms of said passageways midway their lengths are high and slant downwardly towards the ends of said passageways, placing an inductor bar in each of said passageways and making said bars of a size and configuration so that the bottoms of the bars rest upon the bottoms of the slots forming the passageways and the bars are loose in said passageways with the exception of the upper ends of the bars which fit snugly within the reduced width portion of the plate slot outer open ends, making said inductor bars of a length greater than the length of the core so that said bars have extending ends beyond the ends of the core passageways, providing means at the opposite ends of said core to snugly receive the extending ends of the bars to support and hold said bars in a plane parallel to the plane of the longitudinal axis of said shaft, machining the outer peripheral faces of said plates to provide a core which is a true circle, and continuing said machining operation until the top edges of the bars and the peripheral faces of the plates are in alignment to provide a rotor which is smooth and unbroken throughout the entire extent of its outer surface.

3. The method of manufacturing rotors for electric motors which includes the steps of forming a plurality of plates each provided with a plurality of radially extending slots having rounded bottoms and open tops of reduced size, assembling a plurality of said plates to form a laminated core, forming a plurality of inductor bars having at their upper and lower edges longitudinally extending fins which are of reduced thickness in respect to the remaining central portion of the bars, making said bars longer than the core but limiting the length of the fins to the length of the core, inserting one of said bars in each of the slots of said core with the bottom fin of the bar resting upon the rounded bottom of the slot and the top fin of the bar extending snugly into the reduced open ends of the slots, making the extremethickness of said bars and the height of said upper fins such as to permit the bars to be freely movable both longitudinally and vertically in said core slots, positioning said bars so that they have ends extending beyond each end of the core, forming a pair of end rings with openings of a size to snugly receive the extending ends of the bars, placing an end ring at each end of the core and over the extending ends of the bars, clamping the extending ends of the bars against the outer faces of the end rings to hold said rings in abutting relationship with the ends of the core to hold the bars against longitudinal and vertical movement, and machining the outer surface of the core until the core is a true circle and the upper top edges of the top fins of the bars are smooth and flush with the outer face of the core.

4. The method of making an electric motor rotor of the open slot type which comprises, providing a shaft, forming in plates an opening for said shaft and a series of radially extending slots having open ends of reduced width positioned at the outer peripheral face of said plates, assembling a group of said plates on said shaft to provide a laminated core rotatable with said shaft, arranging said plates so that their slots are in intercommunicating relation to form passageways extending transversely through said core in a plane parallel to the longitudinal axis of the shaft, placing an inductor bar in each of said passageways and making said bars of a size and configuration so that the bottoms of the bars rest upon the bottoms of the slots forming the passageways and the bars are loose in said passageways with the exception of the upper ends of the bars which fit snugly within the reduced width portion of the plate slot outer open ends, machining the outer peripheral faces of said plates to provide a core which is a true circle, and continuing said machining operation until the top edges of the bars and the peripheral faces of the plates are in alignment to provide a rotor which is smooth and unbroken throughout the entire extent of its outer surface.

5. The method of making an electric motor rotor of the open slot type which comprises, providing a shaft, forming in plates an opening for said shaft and a series of radially extending slots having open ends of reduced width positioned at the outer peripheral face of said plates, assembling a group of said plates on said shaft to provide a laminated core rotatable with said shaft, arranging said plates so that their slots are in inter-communicating relation to form passageways extending transversely through said core in a plane parallel to the longitudinal axis of the shaft but extending at an angle transverse thereof with the result that the bottoms of said passageways midway their lengths are high and slant downwardly towards the ends of said passageways, placing an inductor bar in each of said passageways and making said bars of a size and configuration so that the bottoms of the bars rest upon the bottoms of the slots forming the passageways and the bars are loose in s id passageways with the exception of the upper ends of the bars which fit snugly within the reduced width portion of the plate slot outer open ends, making said inductor bars of a length greater than the length of the core so that said bars have extending ends beyond the ends of the core passageways, providing means at the opposite ends of said core to snugly receive the extending ends of the bars to support and hold said bars in a plane parallel to the plane of the longitudinal axis of said shaft, machining the outer peripheral faces of said plates to provide a core which is a true circle, and continuing said machining operation until the top edges of the bars and the peripheral faces of the plates are in alignment to provide a rotor which is smooth and unbroken throughout the entire extent of its outer surface.

6. The method of making an electric motor rotor of the open slot type which comprises, providing a shaft, forming in plates an opening for said shaft and a series of radially extending slots having open ends of reduced width positioned at the outer peripheral face of said plates, assembling a group of said plates on said shaft to provide a laminated core rotatable with said shaft, arranging said plates so that their slots are in inter-communicating relation to form passageways extending transversely through said core in a plane parallel to the longitudinal axis of the shaft, placing an inductor bar in each of said passageways and making said bars of a size and configuration so that the bottoms of the bars rest upon the bottoms of the slots forming the passageways and the upper ends of the bars fit snugly within the reduced width portion of the plate slot outer open ends, machining the outer peripheral faces of said plates to provide a core which is a true circle, and continuing said machining operation until the top edges of the bars and the peripheral faces of the plates are in alignment to provide a rotor which is smooth and unbroken throughout the entire extent of its outer surface.

7. The method defined in claim 6 which includes, varying the electrical resistance of the rotor by reducing the height of the inductor bars at a plurality of separated points throughout the lengths of said bars but leaving said bars with their normal height at a point central of their length to provide means for engaging the bottoms of the core slots for supporting the bars.

8. The method of manufacturing rotors for electric motors which includes the steps of forming a plurality of plates each provided with a plurality of radially extending slots having rounded bottoms and open tops of reduced size, assembling a plurality of said plates to form a laminated core, forming a plurality of inductor bars having at their upper and lower edges Iongitudinally extending fins which are of reduced thickness in respect to the remaining central portion of the bars, inserting one of said bars in each of the slots of said core with the bottom fin of the bar resting upon the rounded bottom of the slot and the top fin of the bar extending snugly into the reduced open ends of the slots, machining the outer peripheral faces of said plates to provide a core which is a true circle, and continuing said machining operation until the top edges of the bars and the peripheral faces of the plates are in alignment to provide a rotor which is smooth and unbroken throughout the entire extent of its outer surface.

HARRY EDWARD PAN CHER. 

